For the Potato and Onion Rösti with Triple Caviar, first peel the potatoes, grate coarsely. Peel and dice the onions. Mix both with flour, eggs, salt, pepper. Roast 8 rösti in lard.
Wash lemon well with hot water, dry, grate peel. Stir zest, 3 tablespoons juice with sour cream or crème fraîche. Rinse lettuce leaves, dry.
Serve potato and onion rösti with triple caviar, lemon sour cream, lettuce leaves, chervil.